Preparation And Electrochemical Properties Of Two-dimensional Porous Cobalt/Zinc Sulfides

Due to the serious problems of population growth and environmental pollution,the demand for clean energy production and utilization is very urgent and will continue to grow.The energy crisis has driven the demand for new and innovative materials for developing alternative energy sources and manufacturing innovative energy storage devices.As a new type of green,clean and efficient energy storage device,supercapacitor is a potential charge storage device with high power density,long cycle life and environmental friendliness Therefore,it can be used as a bridge to cross the power gap between traditional capacitor and battery or fuel cell,and it is the best choice for efficient energy storage in electrochemical energy storage system.Generally speaking,the electrochemical performance of supercapacitors is particularly related to the choice of electrode materials.Transition metal sulfide(TMS)has become a potential electrode material due to its good conductivity,high specific capacity,low electronegativity and redox activity.In addition,the large specific surface area of two-dimensional nanostructure can provide more active sites for electrochemical reaction,so as to ensure more sufficient redox reaction.Therefore,a simple and low-cost method to prepare sulfide sheet with two-dimensional porous structure as electrode material has certain research significance and practical application value.In this paper,cobalt sulfide,zinc sulfide and cobalt/zinc bimetallic sulfide were successfully prepared by a simple template free hydrothermal synthesis method.The crystal structure and microstructure of the materials were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area analysis(BET),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)Cyclic voltammetry(CV),galvanostatic charge discharge(GCD)and electrochemical impedance spectroscopy(EIS)were used to characterize the electrochemical properties of the materials.The main work and conclusions of this paper include the following three aspects.1.Preparation and electrochemical properties of two-dimensional porous cobalt sulfide.(1)In the experiment,Co(No₃)₂·6H₂O was used as the catalyst.Three kinds of cobalt sulfide thin films were successfully prepared by direct hydrothermal method with sodium sulfide Na₂S as sulfur source at 120,150 and 180?for 12 h.by observing the electron microscope and comparing the electrochemical CV Curve and GCD curve,it can be found that the S–2 thin films prepared at 150?for 12 h have better morphology and best electrochemical performance.At this time,the specific surface area of the cobalt sulfide sheet is 31.16 m²/g.(2)In terms of electrochemical properties:(1)in the three electrode test,S–2 has higher specific capacity(364 C/g),ratio performance(62.6%)and better cycle stability(77.6%after 10000 charging and discharging at 10 a/g current density);(2)In the two electrode test,the energy density of the hybrid super capacitor(Co S//AC)assembled on the basis of S–2 and AC is 97.6 W/kg,and the energy density of the device can reach 27.9Wh/kg.In addition,after 10000 charging and discharging at the current density of 10 a/g,the initial capacity retention rate of the device can still reach 72%,which shows a good cycle performance.2.Preparation and electrochemical properties of two-dimensional porous zinc sulfide.(1)In the experiment,the controllable synthesis of zinc sulfide was realized by simple hydrothermal method.The influence of hydrothermal reaction time on morphology was investigated.The product Zn S(S–2)with a specific surface area of 33.37m²/g was obtained after 12 h at room temperature and it has better performance.(2)In terms of electrochemical properties:(1)in the three electrode test,Zn S electrode has higher specific capacity(327.2 C/g),and there is still 71%initial specific capacity after 10000 cycles;(2)In the two electrode system,the hybrid supercapacitor(S–2//AC)assembled in 2M KOH solution with S–2 as the positive electrode and AC as the negative electrode can achieve an energy density of 25.56 Wh/kg at a power density of 1081.2 W/kg,and has a capacity retention rate of 71%after 10000 charge discharge cycles,indicating its good energy storage performance.3.Preparation and electrochemical properties of two-dimensional porous cobalt/zinc sulfide.(1)In the experiment,two-dimensional porous cobalt/zinc sulfide was synthesized by one-step hydrothermal method with cobalt nitrate and zinc nitrate as cobalt and zinc sources respectively.At the same time,the effect of Zn/Co ratio on the morphology of the products was studied.It was found that the best morphology was obtained when the Zn/Co ratio was 1:1,with a high specific surface area of 43.64 m²/g,which was more suitable for ion transport.(2)In the aspect of electrochemical performance:(1)in the three electrode test,Zn_0.5Co_0.5S showed 614 C/g high specific capacity(1 A/g),high rate performance(77.9%)and excellent cycle performance(90%capacity retention after 10000 cycles);(2)In the two electrode test:Zn_0.5Co_0.5S//AC hybrid supercapacitor assembled with Zn_0.5Co_0.5S as the positive electrode and activated carbon as the negative electrode has an energy density of 49 Wh/kg when the power density is 957 W/kg,and can maintain a power density of23 Wh/kg when the power density is increased nearly 10 times.After 10000 charge discharge cycles,the capacity retention rate of 88%is still maintained and the cycle stability is excellent.